1) Open a new message. Start typing a known address in the "TO" field.
2) As soon as autocomplete presents an option, hit {Enter} 3 times, forcing the previous address off the top of the data entry field.
3) Type a second known address in the "TO" field.
4) As soon as autocomplete presents an option, you have entered the twilight zone...

Try to use up-arrow to scroll back to the first address. On my system, up-arrow does not work. Page-Up key tries to work, but the cursor is stuck on the second email address. Also, there is no vertical scroll bar.

Left-arrow works OK. There are various ways to get out of this twilight mode, including making any change to the second email address. Sometimes making a change to the first email address also terminates this mode.

Not exactly the worst bug in the world, but kind of weird. Does anybody else see this?